Recently I added my first fuel additive (PS- grey bottle) to the current tank I am finishing up. About last week i noticed a chatter coming from either the tensioner pulley or the IP, wasn't sure. I checked out the tensioner and it was not the problem. Its seems I am hearing a chatter from the IP. The only way I found this was by opening the hood and looking at something else while the engine was idling. I can't hear the chatter from the cab, and can barely hear it with the hood closed (if I listen carefully). I have the stock timing chain installed, which I hear phaser gears can cause this chatter. Is my IP failing or is it the FSD, or something else? Anybody have ideas? I have about 153K miles on the engine right now. The IP was replaced under warranty back in probably 1998 or so.